Numerous hydrogen production chemistries have been explored for portable systems such as sodium borohydride or methanol reforming, however hydrogen storage commercialization has been limited to high-pressure tanks and metal hydrides—both of which have significant usability issues.
The usability challenges of hydrogen storage and generation has limited the wide-scale adoption of on-board hydrogen production chemistries. Although molecular hydrogen has a very high energy density on a mass basis, as a gas at ambient conditions it has very low energy density by volume. The techniques employed to provide hydrogen to portable and on-board applications are widespread, including high pressure and cryogenics, but they have most often focused on chemical compounds that reliably release hydrogen gas on-demand. Often, the focus has been on three broadly accepted mechanisms used to store hydrogen in materials: absorption, adsorption, and chemical reaction.
In absorptive hydrogen storage for fueling a portable application, hydrogen gas is absorbed directly at high pressure into the bulk of a specific crystalline material, such as a metal hydride or various other frameworks. Most often, metal hydrides, like MgH2, NaAlH4, and LaNi5H6, are used to store the hydrogen gas reversibly. However, metal hydride systems suffer from poor specific energy (i.e., a low hydrogen storage to metal hydride mass ratio) and poor input/output flow characteristics. The hydrogen flow characteristics are driven by the endothermic properties of metal hydrides (the internal temperature drops when removing hydrogen and rises when recharging with hydrogen). Because of these properties, metal hydrides tend to be heavy and require complicated systems to rapidly charge and/or discharge them. For example, see U.S. Pat. No. 7,271,567 for a system designed to store and then controllably release pressurized hydrogen gas from a cartridge containing a metal hydride or some other hydrogen-based chemical fuel. This system also monitors the level of remaining hydrogen capable of being delivered to the application by measuring the temperature and/or the pressure of the metal hydride fuel itself and/or by measuring the current output of the fuel cell to estimate the amount of hydrogen consumed.
In adsorption hydrogen storage for fueling a portable application, molecular hydrogen is associated with the chemical fuel by either physisorption or chemisorption. Chemical hydrides, like lithium hydride (LiH), lithium aluminum hydride (LiAlH4), lithium borohydride (LiBH4), sodium hydride (NaH), sodium borohydride (NaBH4), and the like, are used to store hydrogen gas non-reversibly. Chemical hydrides produce large amounts of hydrogen gas upon its reaction with water as shown below:NaBH4+2H2O→NaBO2+4H2 
To reliably control the reaction of chemical hydrides with water to release hydrogen gas, a catalyst must be employed along with tight control of the water's pH. Also, the chemical hydride is often embodied in a slurry of inert stabilizing liquid to protect the hydride from early release of its hydrogen gas. The chemical hydride systems shown in U.S. Pat. Nos. 7,648,786; 7,393,369; 7,083,657; 7,052,671; 6,939,529; 6,746,496; and 6,821,499, exploit at least one, but often a plurality, of the characteristics mentioned above.
In chemical reaction methods for producing hydrogen for an application, often hydrogen storage and hydrogen release are catalyzed by a modest change in temperature or pressure of the chemical fuel. One example of this chemical system, which is catalyzed by temperature, is hydrogen generation from ammonia-borane by the following reaction:NH3BH3→NH2BH2+H2→NHBH+H2 
The first reaction releases 6.1 wt. % hydrogen and occurs at approximately 120° C., while the second reaction releases another 6.5 wt. % hydrogen and occurs at approximately 160° C. These chemical reaction methods do not use water as an initiator to produce hydrogen gas, do not require a tight control of the system pH, and often do not require a separate catalyst material. However, these chemical reaction methods are plagued with system control issues often due to the common occurrence of thermolysis runaway. See, for example, U.S. Pat. No. 7,682,411, for a system designed to thermally initialize hydrogen generation from ammonia-borane and to protect from thermal runaway. See, for example, U.S. Pat. Nos. 7,316,788 and 7,578,992, for chemical reaction methods that employ a catalyst and a solvent to change the thermal hydrogen release conditions.
In view of the above, there is a need for an improved hydrogen generation system and method that overcomes many, or all, of the above problems or disadvantages in the prior art.